Determining the sequence of a Deoxyribonucleic acid (DNA) molecule is, conventionally, a difficult and expensive chemical process. However, with the rapid growth in nanotechnology, new methods may be devised to increase accuracy, speed, and cost of determining the constituent parts of biological polymers such as proteins, DNA, and ribonucleic acid (RNA).
Various methods have been developed for determining the chemical composition of portions of a DNA strand or the chemical composition of an entire DNA strand. One such method involves creating a micro-array with hundreds or thousands of patches of single stranded DNA, which are often referred to as probes, attached to various locations on a substrate such as glass or silicon.
When using this DNA detection method, the DNA to be examined is first transcribed into RNA. RNA is a chemical very similar to DNA that can encode the same information as DNA. The RNA can then be used to create single stranded DNA (ssDNA) copies of the RNA. Fluorescent molecules, also referred to as tags, are then bonded onto the new single stranded DNA molecules.
When these tagged single stranded DNA molecules are washed over the micro-array, they will bond and stick to any of the single stranded DNA probes having a gene sequence with bases that are complementary to, but arranged in the same order as, the bases of the tags. Then, a light source exposing the micro-array causes the tagged DNA molecules that have stuck to the micro-array to fluoresce. The fluorescent glow can be detected and, based on where the various DNA tags were placed and their corresponding sequence, the sequence of the portion of the DNA stuck to that site can be determined.
Unfortunately, this process requires a significant number of chemical and optical steps to determine various portions of a DNA sequence. In addition, the detection is limited to the variety of DNA probes on the micro-array. Long probes, with a large number of sequences can detect a significant match, but it becomes difficult to place every possible variation of long probes on a single micro-array. On the other hand, short probes may be incapable of detecting a desired long sequence.
Another proposed detection method involves examining a polymerase chain reaction replication process. An RNA polymerase may attach to a DNA molecule and begin separating the DNA strand. The RNA polymerase then traverses along the DNA strand opening newer regions of the DNA strand and synthesizing an RNA strand matching the opened portions of the DNA. As the RNA polymerase traverses along the DNA, the portion of the DNA opened by the RNA polymerase closes down and re-bonds after leaving the RNA polymerase. In this detection method, the RNA polymerase is attached to an electronic device, such as a single electron transistor. Whenever the polymerase replication takes place, a charge variation may occur on the single electron transistor for each portion of the DNA molecule opened up by the RNA polymerase. By detecting these charge variations, the composition of the portion of the DNA molecule that is transcribed can be determined.
Unfortunately, the polymerase chain reaction method relies on the occurrence of this biological process of replication. In addition, the RNA polymerase replication only begins and ends at certain defined points of the DNA strand. As a result, it may be difficult to discover all portions of the DNA strand to be examined.
A device and method with the flexibility to examine the entire sequence of a DNA strand, without requiring complicated chemical and optical processing, is needed. A molecule detection system using nanoelectronic devices without the requirement of a biological replication process may be a smaller and less costly system than conventional approaches. This integrated molecule detection system would be easier to use and may be adaptable to detect a variety of predetermined sets of bases within DNA molecules. Furthermore, this molecule detection system may be integrated with other electronic devices for further analysis and categorization of the detected molecules.